Greek labor unions staged a 24-hour strike on Thursday that canceled hundreds of flights, shut public offices and severely disrupted local transport, in the first major industrial action to cripple the austerity-weary country in months.

Private sector union GSEE and its public sector counterpart ADEDY called the walkout to protest against planned layoffs and pension reform demanded by European Union and International Monetary Fund lenders who have bailed out Greece twice.

All Greek domestic and international flights were canceled after air traffic controllers joined the strike. Trains and ferries also halted services. Hospitals worked on emergency staff while tax and other local public offices remained shut.

“GSEE is resisting the dogmatic obsession of the government and the troika with austerity policies and tax hikes,” the union said in a statement this week.

It accused the government of trying to take the labor market back to “medieval times” and of implementing policies that are causing a “humanitarian crisis.”

Thousands of Greeks were preparing to march to parliament later on Thursday as part of rallies to mark the strike.

The two unions last held a general strike in April. Major protests have declined sharply since then as frustration and anger give way to a mood of despondency and resignation over a jobless rate exceeding 25 percent and a sharp fall in incomes.

Turnout at Thursday's rallies could provide a key measure of the opposition facing Prime Minister Antonis Samaras's conservative-led government, which is under pressure from EU and IMF lenders to impose more cutbacks to balance next year's budget.

Samaras has imposed repeated rounds of austerity to ensure Greece continues to receive aid payments but is now trying to abandon the unpopular bailout program in a bid to secure his government's survival through next year.

In a setback to those plans, Greek officials returned empty-handed from Paris on Wednesday after two days of talks with EU and IMF inspectors failed to clinch a deal on the country's final bailout review.